1. Field of the Invention
The present invention relates in general to valve actuation devices of an internal combustion engine, and more particularly to valve actuation devices of a type that eliminates or at least minimizes dispersion in a valve lift degree of intake and/or exhaust valves of the engine.
2. Description of the Related Art
In order to clarify the task of the present invention, one known valve actuation device of an internal combustion engine will be briefly described, which is shown in Japanese Laid-open Patent Application (Tokkai) 2002-38913.
The valve actuation device of the publication generally comprises a drive shaft that is synchronously rotated by a crankshaft, an eccentric drive cam that is mounted on the drive shaft, and two swing cams that open and close two intake valves for each cylinder. The two swing cams are rotatably disposed on the drive shaft having the eccentric drive cam put therebetween.
A multi-link type power transmission mechanism is further provided for each cylinder, which swings the two swing cams by receiving a power from the eccentric drive cam.
The multi-link type power transmission mechanism generally comprises a rocker arm that is arranged above an intermediated position of the two swing cams and swingably disposed on a control shaft, a link arm that pivotally connects an end portion of the rocker arm to the eccentric drive cam and a link rod that pivotally connects a forked other end of the rocker arm to each of the swing cams.
The control shaft extends along a longitudinal axis of the engine, and is rotatably supported by bearings that are arranged on an upper part of a cylinder head of the engine. The control shaft has an eccentric control cam for each cylinder, which serves as a swing fulcrum of the rocker arm.
An electric actuator is further provided, which, in accordance with an operation condition of the engine, turns or pivots the control shaft changing an angular position of the control cam, so that the valve lift degree of each intake valve is varied in accordance with the engine operation condition.
The above-mentioned Laid-open Patent Application proposes several types of power transmission mechanism for achieving the above-mentioned function.